Turbomachine vane comprising an electroacoustic source with improved assembly mode, row of outlet guide vanes and turbomachine comprising such a vane

ABSTRACT

A turbomachine vane includes an electroacoustic source including two membranes fixed on a support arranged such that the membranes and the support delimit a first cavity. The membranes are arranged on two opposite sides of the first cavity between the two aerodynamic surfaces of the vane. A first of the aerodynamic surfaces includes a first region arranged facing a first of the membranes for the passage of acoustic waves. The membranes and membrane vibration device are configured such that the membranes vibrate in phase opposition and along a same emission direction by applying forces to the support such that the resultant force is approximately zero. The mechanical energy lost in the form of vane deformations due to membrane vibrations can thus be minimized.

TECHNICAL DOMAIN

This invention relates to the domain of turbomachine vanes, particularlyfor aircraft turbomachines.

The invention relates in general to a vane comprising an electroacousticsource designed to reduce noise caused by rotation of blinks in aircraftturbomachines.

In some preferred embodiments, the invention is intended particularly toreduce noise caused by fans in twin-spool turbomachines, andparticularly spike noise at partial load caused by the interactionbetween wake from these fans and outlet guide vanes (OGV) downstreamfrom these fans. These outlet guide vanes are affected by the impact ofan air flow that periodically reduces velocity, which induces a periodicvariation to the load applied on these outlet guide vanes, this periodicload variation being the cause of the above-mentioned spike noise.

STATE OF PRIOR ART

It has been proposed that noise caused by fans can be reduced byintroducing an electroacoustic source controlled so as to generate soundwaves in phase opposition to the above-mentioned noise, into statorvanes located downstream from the fans.

Documents [1] to [3] listed at the end of this description showdifferent examples of implementations of this technique.

In order to save energy, the inventors fixed themselves the objective ofoptimising the energy efficiency of this type of technique.

PRESENTATION OF THE INVENTION

The invention discloses a vane for a turbomachine comprising a bodyforming two aerodynamic surfaces, namely an intrados surface and anextrados surface, and an electroacoustic source. The electroacousticsource comprises two membranes fixed on a support fixed to the body orforming part of the body, and means of vibrating these membranes. Thesupport and the membranes jointly delimit a first cavity inside thebody, such that the membranes are arranged on two opposite sides of thefirst cavity.

According to the invention, the membranes are arranged between the twoaerodynamic surfaces. Furthermore, a first aerodynamic surface among thetwo aerodynamic surfaces comprises a first region arranged facing afirst membrane among the membranes and allowing the passage of acousticwaves. Finally, the membranes and the membrane vibration means areconfigured such that the membranes vibrate in phase opposition and alonga same emission direction by applying forces to the support such thatthe resultant force is approximately zero.

In general, the invention thus arranges matters such that forces appliedto the support locally by the membranes, in reaction to vibrationmovements of the membranes, are compensated within the support such thatno resultant of these forces is transmitted to other parts of the vane.Thus, a maximum part of the mechanical energy supplied to the membranesby the membrane vibration means is actually used to vibrate themembranes, while mechanical energy lost in the form of deformations ofthe vane body can be minimised.

According to other advantageous aspects of the invention, the methodcomprises one or several of the following characteristics, taken inisolation or in any technically possible combination:

a second aerodynamic surface among the two aerodynamic surfacescomprises a second region arranged facing a second membrane among themembranes and allowing the passage of acoustic waves.

a second membrane among the membranes, and at least one among the bodyand the support, jointly delimit a second cavity separated from thefirst cavity, the second cavity opening up through at least one openingon the side of the first aerodynamic surface, and the second cavitybeing closed on the opposite side;

the membranes are similar, and the membrane vibration means areconfigured such that the amplitudes of the membrane vibrations are thesame;

the membranes are symmetric with each other about a plane of symmetryorthogonal to the emission direction;

the first cavity is approximately symmetrical about the plane ofsymmetry;

the first cavity is connected to a pressure balancing conduit;

the first cavity is closed.

The invention also relates to an annular row of outlet guide vanes for aturbomachine, comprising at least one vane of the type described above.

The invention also relates to a turbomachine comprising at least onevane of the type described above or an annular row of outlet guide vanesof the type described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and other details, advantagesand characteristics of it will become clear after reading the followingdescription given as a non-limitative example with reference to theappended drawings in which:

FIG. 1 is a partial diagrammatic axial sectional half-view of atwin-spool turbomachine for an aircraft;

FIG. 2 is a partial diagrammatic sectional view of an outlet guide vaneaccording to a first preferred embodiment of the invention, forming partof the turbomachine in FIG. 1;

FIGS. 3 to 5 are views similar to FIG. 2, each illustrating outlet guidevanes according to other preferred embodiments of the invention.

In all these figures, identical numeric references may denote identicalor similar elements.

DETAILED PRESENTATION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates a part of aircraft twin-spool turbomachine 10comprising particularly a fan 12, a low pressure compressor 14 and ahigh pressure compressor 16 arranged in a space 18 carrying a core flow20 of the turbomachine, and an annular row 22 of outlet guide vanesextending through a space 24 carrying a bypass flow 26 of theturbomachine delimited at the exterior by a nacelle 28 of thisturbomachine.

Throughout this description, the axial direction X is the direction of alongitudinal axis A of the turbomachine corresponding to an axis ofrotation of the turbomachine rotors, the radial direction R is adirection orthogonal to the axial direction X at all points andintersecting the X direction, and the tangential direction T isorthogonal to the above two directions at all points. Furthermore, the“upstream” and “downstream” directions are defined with reference to thegeneral flow of gases in the turbomachine.

The annular row 22 of outlet guide vanes comprises a set of vanes, atleast some of these vanes incorporating an electroacoustic source 32.

In a manner known in itself, the turbomachine comprises control means 34to control the electroacoustic 32 sources of each of the outlet guidevanes, said means being configured so as to minimise a magnitudemeasured by one, or preferably several, acoustic sensors 36.

The magnitude minimised by the control means 34 can be the global soundintensity or the sound intensity measured in a predetermined frequencyband, for example in a frequency band centred on the rotation frequencyof the turbomachine fan 12.

The control means 34 may for example be housed in the nacelle 28, andcomprise an electronic unit 38 designed to receive information fromacoustic sensors 36 and to use an algorithm for controlling theelectroacoustic source 32 of each vane 30, according to the principle ofa feedback loop.

The acoustic sensors 36 are advantageously integrated into the nacelle28, for example close to its upstream end, in other words at theturbomachine intake duct, to enable a measurement of noise emitted inthe upstream direction by the fan 12. As a variant, some or all of theacoustic sensors 36 can be arranged at a secondary nozzle of theturbomachine (not visible on FIG. 1) to enable a measurement of noiseemitted in the downstream direction by the fan 12.

During operation, interaction between the wake generated by the bladesof the rotating fan 12 and vanes in the annular row 22 of outlet guidevanes can be the source of emitted sound waves W1 propagating in theupstream and downstream directions from the blades of the fan 12.

The electroacoustic source 32 of each vane 30 in the annular row 22 ofoutlet guide vanes is controlled to generate sound waves W2 so as toinduce destructive interference with sound waves W1 originating from thefan 12, so as to minimise the sound intensity measured by the acousticsensors 36.

FIG. 2 illustrates part of a vane 30 according to a first embodiment ofthe invention in more detail, this vane 30 being intended to form partof the annular row 22 of outlet guide vanes of the turbomachine 10 inFIG. 1. FIGS. 3-5 illustrate the vanes 30 of other preferred embodimentsof the invention, as will become clearer in the following.

On FIGS. 2-5, the axial direction X corresponds to the direction of thelongitudinal axis A of the turbomachine 10 when the vane 30 isintegrated into the annular row 22 of outlet guide vanes within theturbomachine 10. Under the same conditions, the direction from the root(not shown) of the vane 30 towards the tip of the vane (not shown),called the wingspan direction WS of the vane, coincides with the radialdirection R.

The vane 30 comprises a body 40 forming two aerodynamic surfaces, theintrados 42 and extrados 44 surfaces respectively, and comprises theabove-mentioned electroacoustic source 32.

The electroacoustic source 32 comprises two membranes 46A, 46B andmembrane vibration means 48.

The membranes 46A, 46B are fixed to a support 50. In the embodiment inFIG. 2, and in the embodiments in FIGS. 4 and 5, the support 50 iscomposed of a part of the body 40.

As a variant, the support 50 may be an element distinct from the body40, and installed in an opening of the body, for example by embedment asshown on FIG. 3.

The vibration means 48 are composed for example of two piezoelectricplates 48A, 48B applied to central regions of the two membranes 46A, 46Brespectively so as to form two bimetallic assemblies. In such anassembly, an elongation of the piezoelectric plate induces a deformationof the membrane, in a well-known manner. On FIGS. 2-5, the membranes46A, 46B are thus represented in a rest conformation in continuouslines, and in an elongated configuration in discontinuous linesreferences 46A1 and 46B1 respectively.

The membranes 46A, 46B are fixed to the support 50 by theircorresponding peripheries.

The support 50 and the membranes 46A, 46B jointly delimit a first cavity52 inside the body 40, such that the membranes 46A, 46B are arranged ontwo opposite sides of the first cavity 52.

According to the most general principle of the invention, the membranes46A, 46B are arranged between the two aerodynamic surfaces 42 and 44.

Furthermore, a first aerodynamic surface among the two aerodynamicsurfaces, for example the intrados surface 42, comprises a first region54 arranged facing a first membrane 46A among the membranes and allowingthe passage of acoustic waves.

Finally, the membranes 46A, 46B and the membrane vibration means 48 areconfigured such that the membranes vibrate in phase opposition and alonga same emission direction E (preferably parallel to the axial directionX) by applying forces to the support 50 such that the resultant of theforces FA, FB is approximately zero. “Phase opposition” means that whenone of the membranes is moving in one direction, for example towards theleft on the figures, the other membrane moves in the other direction,for example towards the right in the figures.

This latter characteristic is made possible particularly by the factthat the membranes 46A, 46B are laid out between the two aerodynamicsurfaces 42 and 44, such that the shapes and orientations of themembranes 46A, 46B respectively are not imposed by the shapes of theaerodynamic surfaces 42 and 44 respectively.

In general, the invention thus arranges matters such that forces appliedto the support 50 locally by the membranes 46A, 46B, in reaction tovibration movements of the membranes, are compensated within the support50, which is either a part of the body 40 relatively close to themembranes 46A, 46B, or an element distinct from the body. Thus, noresultant of these forces is transmitted to the remaining part of thebody 40 or to the entire body, depending on the case. Consequently, amaximum proportion of the mechanical energy output to the membranes 46A,46B by the vibration means 48 is effectively used to vibrate themembranes, while mechanical energy lost in the form of deformations ofthe body 40 is minimised.

To achieve such a result, it is advantageous if the membranes 46A, 46Bare similar, and the means of vibrating the membranes 46A, 46B areconfigured such that the amplitudes of membrane vibrations are the same.

Nevertheless, other configurations are possible so as to cancel out theresultant force of forces FA and FB.

For example, one of the membranes may be smaller than the other membranebut have a larger surface area than the other membrane such that itsmass is globally the same as the mass of the other membrane.

As a variant, the mass of one of the membranes may be smaller than themass of the other membrane, but its vibration amplitude may be largerthan that of the other membrane.

In all cases, the resultant of the forces FA and FB is cancelled outwhen the product of the mass and the acceleration of one of themembranes (integrated on the surface of the membrane) is equal to theproduct of the mass and the acceleration of the other membrane (alsointegrated on the surface of this other membrane).

Furthermore, the membranes 46A, 46B are preferably symmetric with eachother about a plane of symmetry P orthogonal to the emission directionE, as shown on FIGS. 2-5

Consequently, the membranes 46A, 46B are centred on the same emissionaxis EA, which also has also an additional advantage of minimising themoment resultant of forces FA and FB. The reduction in the mechanicalenergy dissipated by deformation of the body 40 of the blade is thusoptimal.

Furthermore, the first cavity 52 is preferably approximately symmetricalabout the plane of symmetry P, as can also be seen on FIGS. 2-5.

This latter symmetry characteristic optimally simplifies force pathsbetween the membranes 46A, 46B and the support 50.

In the embodiments in FIGS. 2, 3 and 5, the first cavity 52 is connectedto a pressure balancing duct 56 that for example opens up in theintrados surface 42.

The pressure balancing duct 56 can balance the internal pressure in thefirst cavity 52 with the pressure in the environment outside the vane30, such that the deformation of the membranes 46A, 46B is not disturbedby the pressure inside the first cavity 52.

Thus, the pressure balancing duct 56 can in general simplify control ofmembrane vibration means 48.

As a variant, the first cavity can be closed as shown on FIG. 4.

It should be noted that the concept of a first cavity being“approximately symmetrical” about the plane of symmetry means that thefirst cavity 52 is symmetric about the plane of symmetry P, ignoring theconnection of the cavity to the pressure balancing duct 56, ifapplicable.

In the embodiments in FIGS. 2-4, a second aerodynamic surface among thetwo aerodynamic surfaces, for example the extrados surface 44, comprisesa second region 58 arranged facing a second membrane 46B among themembranes and allowing the passage of acoustic waves.

Acoustic waves generated by the two membranes are thus transmittedthrough the two aerodynamic surfaces 42 and 44 respectively, propagatingoutside the vane in opposite directions.

On the other hand, in the embodiment shown on FIG. 5, the body 44, thesupport 50, and a second membrane 46B among the two membranes mentionedabove, jointly delimit a second cavity 60 separated from the firstcavity 52. The second cavity 60 opens up through an opening 62 on theside of the first aerodynamic surface or intrados surface 42, in otherwords on the same side as the first membrane 46A. Furthermore, thesecond cavity 60 is closed on the opposite side, namely on the side ofthe extrados surface 44.

Thus, instead of the acoustic wave emitted by the second membrane 46Bpropagating outside the vane in a direction opposite the propagationdirection of the wave emitted by the first membrane 46A, the acousticwave emitted by the second membrane 46B propagates inside the secondcavity 60 so as to be reflected towards the first aerodynamic surface orintrados surface 42, passing through the opening 62. The acoustic waveemitted by the second membrane 46B then interferes constructively withthe acoustic wave emitted by the first membrane 46A, provided that thereis an appropriate phase shift between the opening 62 and the firstmembrane, and appropriate sizing of the second cavity 60. Such a phaseshift is materialised on FIG. 5 by the offset D between the opening 62and the first membrane 46A along the emission direction E.

In this case, the first aerodynamic surface or intrados surface includesa third region 64 located facing the opening 62 and allowing the passageof acoustic waves. The third region 64 and the first region 54 can becontiguous, as shown on FIG. 5.

As a variant, and depending on the respective shapes of the support 50,the body 40 and the second cavity 60, the second cavity can be entirelydelimited by the second membrane 46B and the body 40, or by the secondmembrane 46B and the support 50.

Furthermore, the acoustic efficiency of the second membrane 46B can beoptimised by forming the opening 62 at the end of a throat 66 sized toform a Helmholtz resonator.

Moreover, regardless of the configuration (through or not through) ofthe electroacoustic source 32, the pressure fluctuation that occursinside the first cavity 52 can be used to produce an additional acousticsource at the outlet from the pressure balancing duct 56 byappropriately sizing this duct so that it forms a Helmholtz resonator,as shown diagrammatically on FIG. 5.

In this case, the pressure balancing duct 56 can open up through aninternal wall 68 of the vane, at a distance from the correspondingaerodynamic surface 42, in which case the latter comprises anotherregion 70 formed facing the outlet from the pressure balancing duct 56through which acoustic waves can pass.

In the example illustrated, optionally, the internal wall 68 has thesame offset D relative to the first membrane 46A, along the emissiondirection E, as the opening 62 mentioned above.

Other variants are possible without going outside the framework of theinvention defined by the appended claims, particularly any technicallyfeasible combination of characteristics of the embodiments in FIGS. 2-5.

For example, the vane in the non-through configuration in FIG. 5 may nothave a pressure balancing duct and/or may be provided with a supportseparate from the body 40 of the vane.

In general, each of the regions configured to allow the passage ofacoustic waves may for example consist of an opening formed in thecorresponding aerodynamic surface of the vane, this opening preferablybeing covered by a woven fabric or a wall containing microperforations.

BIBLIOGRAPHY

-   [1]: ZILLMANN J ET AL. “Active Control of Fan Noise by Active    Stators” INTERNOISE 2001: THE 2001 INTERNATIONAL CONGRESS AND    EXHIBITION ON NOISE CONTROL ENGINEERING, Aug. 27 2001 (2001-08-27),    pages 701-706, XP008139301, The Hague;-   [2]: GENOULAZ N ET AL: “Experimental Validation of an Active Stator    Technology Reducing Turbofan Engine Noise”, 13^(th) AIAA/CEAS    AEROACOUSTICS CONFERENCE, AIAA 2007-3688, AMERICAN INSTITUTE OF    AERONAUTICS AND ASTRONAUTICS, May 21 2007 (2007-05-21), pages 1-18,    XP008139275, RESTON, Va. ISBN: 978-1-56347-883-3-   [3]: Patent application FR 2 968 048 A1

1. A vane for a turbomachine comprising a body forming two aerodynamicsurfaces, namely an intrados surface and an extrados surface, and anelectroacoustic source, wherein the electroacoustic source comprises twomembranes fixed on a support fixed to the body or forming part of thebody, and means of vibrating the membranes, and wherein the support andthe membranes jointly delimit a first cavity inside the body, themembranes being arranged on two opposite sides of the first cavity,wherein the membranes are arranged between the two aerodynamic surfaces,a first aerodynamic surface among the two aerodynamic surfaces comprisesa first region arranged facing a first membrane among the membranes andallowing the passage of acoustic waves, and membranes and the membranevibration means are configured such that the membranes vibrate in phaseopposition and along a same emission direction, by applying forces tothe support such that the resultant force of said forces isapproximately zero.
 2. The vane according to claim 1, wherein a secondaerodynamic surface among the two aerodynamic surfaces comprises asecond region arranged facing a second membrane among the membranes andallowing the passage of acoustic waves.
 3. The vane according to claim1, wherein a second membrane among the membranes, and at least one ofthe body and the support, jointly delimit a second cavity separated fromthe first cavity, the second cavity opening up through at least oneopening on the side of the first aerodynamic surface, and the secondcavity being closed on the opposite side.
 4. The vane according to claim1, wherein the membranes are similar, and the means of vibrating themembranes are configured such that the amplitudes of membrane vibrationsare the same.
 5. The vane according to claim 4, wherein the membranesare symmetric with each other about a plane of symmetry orthogonal tothe emission direction.
 6. The vane according to claim 5, wherein thefirst cavity is approximately symmetrical about the plane of symmetry.7. The vane according to claim 1, wherein the first cavity is connectedto a pressure balancing duct.
 8. The vane according to claim 1, whereinthe first cavity is closed.
 9. An annular row of outlet guide vanes fora turbomachine, comprising at least one vane according to claim
 1. 10. Aturbomachine, comprising at least one vane according to claim 1.